Bring water to a boil in a pot. Plunge the tomatoes and cook for 5 minutes. Drain them, peel, cut into cubes and set aside. Peel and chop the onion and garlic and place in a large nonstick skillet with oil and cook for 5 minutes until lightly browned. Meanwhile, under running water clean the prawns, dry them, place them in the pan, salt lightly, cover with a lid and cook for 3 minutes over low heat. Remove the lid, remove the prawns and set aside. To the remaining liquid in the pan add wine and, after raising the flame, let it evaporate almost completely before adding the chopped tomatoes. Add some salt and continue cooking of very low fire for 20 minutes from the moment the sauce begins to boil. After this, add a few tablespoons of warm water, put the prawns in the pan, cover with the lid and cook for 7 minutes. Before serving, season with plenty of black pepper.